The muscular layer of the heart (myocardium) contracts and relaxes to pump blood throughout the body. Oxygen poor blood from the body enters into the right atrium then flows into the right ventricle. The right ventricle pumps the blood to the lungs where gas exchange occurs. The oxygen rich blood is then returned to the left atrium and into the left ventricle. The left ventricle pumps the oxygen rich blood into the aorta which distributes the blood throughout the entire body. This process keeps repeating.
